Sheet metal article and method of forming the same



Jan.14,1947. o. A. WHEELON SHEET METAL ARTICLE AND METHOD OF FORMING THE SAME Filed June 20, 1942 2 Sheets-Sheet 1 INVENTOR 7 BY l ATTORNEY Jan. 14, 1947. WHEELON 2,414,346

SHEET METAL ARTICLE AND METHOD OF FORMING THE SAME Filed June 20, 1942 2 Sheets-Sheet 2 INVENTOR ATTORNEY Patented Jan. 14, 1947 SHEET METAL ARTICLE AND METHOD OF FORMING THE SAME Orville A. Wheelon, Pacific Palisades, CaliL, assignor to Douglas Aircraft Company, Inc., Santa Monica, Calif., a corporation of Delaware Application June 20, 1942, Serial No. 447,760

Claims. 1

. This invention relates to sheet metal articles and method of making the same, and relates particularly to the art of making sheet metal articles involving pressing a plate of sheet metal against a rigid former block by a press head faced with rubber or other elastically deformable material, the plate being shaped to provide marginal portions, overhanging the face of the block, which are bent downward around the edges of the block and against its sides by the rubber facing in the press head. One such method for forming sheet metal articles is shown and described in Patent No. 2,190,659 to H. E. Guerin, dated February 20, 1940. a

In practicing this method of forming sheet metal articles, difiiculty has been experienced in bending the marginal portions of the sheet metal over non-rectilinear edges or shoulders of forming blocks without producing undesirable deformations, such as wrinkles or folds. These deformations appear in the bent portions of the sheet metal articles formed in this manner because of the resistance to thickening under compressive stresses of the metal material, particularly of certain alloys. Since the metal will not thicken under the compressive stresses applied to it in the forming process, folds and wrinkles are produced. It then becomes necessary for the operator to remove these wrinkles by hand forming. The greater the departure of the forming block edge from rectilinear state, the larger or more numerous become the wrinkles or folds.

It is an object of the invention to avoid formation of these folds, wrinkles, or other deformations during shaping of the finished product and to provide a simple method of producing a sheet metal article having walls disposed at an angle to each other which are smoothly contoured and preferably of substantially uniform thickness.

It is another object of the invention to accomplish, without use of hand finishing the elimination of wrinkles or folds in the walls of the completed article by providing for displacement of the excess metal, which otherwise appears in the deformations, from that portion of the article in which it is initially present, to another portion, where this excess metal may be accommodated in a predetermined disposition, without disadvantage to the completed article. By hand finishing is meant hand fabrication of the article after it is taken from the forming press, such as hammering the flanges or use thereon of a metal shrinking device such as now in use.

It is another object of the invention to provide a formed article and a method of forming the same characterized by displacement of the excess metal from a location where it would otherwise form wrinkles, to a location where it serves the desirable object of strengthening or stiffening that section of the wall of the article with respect to which it is displaced.

More specifically, it is an object of the invention .to provide in the fabricationof flanged sheet metal articles in which the flange of the article extends along a curvilinear edge, bulges so placed in the web of the article that the excess of metal entering into the formation of these bulges may be supplied by displacement from the flange, wherein otherwise an equivalent excess of metal would produce wrinkles,

It is another more specific object of the invention to provide, in forming flanged sheet metal articles in which the flange has an inset portion or joggle, for the displacement of the excess metal in the flange to a bulge or protuberance in the web of the proper size and configuration to prevent the formation of wrinkles in the flange.

It is another object to provide a method of determining the shape and dimensions of the displacement protuberances in the web of flanged articles for the accomplishment of the aforesaid purposes.

Other objects and advantages of the invention will be apparent from the following description and accompanying drawings and from the claims.

In the drawings, which are for illustrative purposes only,

Fig. l is a fragmentary perspective view of an airplane rib showing a flanged article in the manufacture of which this invention may be practiced.

Fig. 2 is a perspective view of a. nose section of an airplane rib, commonly termed a nose rib, formed in accordance with prior practice, before hand finishing.

Fig. 3 is a perspective view of a nose rib formed in accordance with this invention.

Fig. 4 is a perspective view of a forming block taken along line 8-8 and '9-9 respectively of the diagram of Fig. '7.

forming block for use in making the portion of an airplane rib shown in Fig. 11.

While the invention may be practiced in make ing many kinds of integral sheet metal articles having two or more, walls angularly related to each other so as to form a dihedral angle at their junction, there has been selected to illustrate an embodiment of the invention a flanged airplane rib such as that shown in Fig. 1 of the drawings and designated thereon with the numeral III. The airplane rib III has a web I4 and a flange I3, forming a dihedral angle therewith the flange being for the purpose of securing the wing skin of the airplane to the wing frame of which the rib is a part. In the upper part of the rib l a notch |0b is shown, and the flange |3 adjacent this notch is provided with an inset or joggle so that the upper face of the transverse structural member l2 will be flush with the upper face of the flange l3. To inhibit the formation of folds and wrinkles in the flange |3 where it extends along a non-rectilinear portion, such as the curved edge of the nose rib, the

flange I3 is divided into short tongue-like sections |3a separated by short spaces or gaps l5.

Where a. flange such as shown at l3 in Fig. 1 is carried around an edge having a short radius of curvature, the formation of the flange into separate sections or tongues l'3a often fails to prevent buckling or wrinkling. As an example,

I have shown in Fig. 2 a web l4 having flange section 3a extending downward from a curved edge having a relatively small radius of curvature. These flange sections |3a are separated from each other by gaps or spaces l 5 ending with recesses I 9 formed in the edge of the web. Under the condition shown, the provision of the gaps l5 has not been effective to prevent formation of wrinkles 20 in the flange sections l3a. Because of the curvature of the edge or shoulder l8a from which the flange section |3a depends downwardly between adjacent spaces l5, there is a reduction in the overall length of the lower designated at 22, which increase the surface area of the web 2| sufiiciently to compensate for the decrease in area of those half portions of flange sections 23 on either side of the gap or space 25 between these flange sections. The bulge 22 is centered around a recess 28 aligned with the space 25, the greatest elevation of the bulge being adjacent the recess 26 and its wall being faired off from the recess 26 inwardly of the web and laterally thereof in either direction alon the edge 21 of the web. a Fig. 4 shows a forming block shapedto produce bulges such as that shown at 22 in the nose 4 rib. It is a rigid block having an upper face 28 and a side wall 29. The plate from which the nose rib is to be formed is cut to proper shape and placed in position upon the face 28. Elevations 3| are provided on the face 28 at spaced intervals along its periphery 32, the spacing corresponding to that of the flange sections 23 and the elevations being aligned with the spaces 25 between the flange sections and the recesses 28 inthe web 2| of the nos rib. When, now, the rubber faced press head is moved downwardly upon the sheet metal plate from which the nose rib is to be formed, the elevations 3| engage the plate initially and as the press head continues to move downwardly, the bulges 22 are formed, the central portion of the plate continuing downwardly into engagement with the face 28 of the former block, after which the marginal portion of the plate is bent downwardly and against the side 29 of the former block. Themetal used to form the bulges 22 is drawn from the flange sections 23, of the nose rib, which are thereby relieved of the excess metal which would otherwise set up compressive stresses upon the contraction of the flange sections as they are bent over the curved periphery of the forming. block. The provision of the elevations 3| on the upper face of the forming block thus entirely eliminates the folds or wrinkles in the flange wall, presenting a smoothly contoured surface, to which may be secured the skin of the airplane wing.

The bulges or elevations 22 in the nose rib occasion no disadvantage when the'nose rib is in- The dimensions, shape, and location of the bulges 22 are critical in character and must be carefully determined. to correspond with the length of the flange sections and the radius of curvature of the joint between the web and flange sections of the nose rib.

I points B and A and between the points B and C.

The point C is midway of two adjacent cut outs. The point A is the point at which the curve in the edge of the web merges into a tangent line or into a curve of such large radius that the flange therealong may b smoothly formed with out the use of notches. If the distances A-B and BC are substantially different. then the height of the displacement should be computed upon the greater distance.

The following procedure may be used to determine the height of the displacement. Draw AH perpendicular to 0A intersecting OB extended, 0 being the center of curvature of the periphery of the web. Draw a line LJ parallel to OH and passing through the end of the cut out, the point J being the intersection of this line with the line a correct height of the displacement elevation or bulge to be formed adjacent this particular cut out to liminate any wrinkles which might otherwise form in the flange at this point,

The displacement elevation must be faired in with the remainder of the web. The dimensions of the faired portion of the elevation are not critical, but, in general, should be such that the increase in surface area of the displacement elevation over its projected plan area is substantially qual to the shrinkage in area of the flange sections adjacent the displacement elevation, as they are bent downwardly from the plane of the web into perpendicular relation with the plane of the web. Fig. 7 is a diagram illustrating a method of laying out the dimensions and shape of the elevation.

If the displacement elevations are too high or too close together, they may merge along the periphery of the web to form a bead, as shown in broken lines in Fig. 9. If they are too far apart or not sumciently high, they fail to serve their purpose and wrinkle appear in the flange sections.

Fig. 10 shows the method of designing the shape of the sheet metal plate from which the nose rib is to be formed.

Line OM is the center line of one of the flanges, the point being the center of the curve of the periphery of the web and this center line crossing the periphery at L. The sides of the flange designated SR are parallel to this center line, and the outer end is perpendicular to the center line. Recesses 26 in the central portion of the plate, that portion which in the forming of the nose rib becomes the web, are disposed with their sides in registry with the sides of the flange sections. X-X represents a section of the periphery of the web between two recesses 26 and ZZ represents the upper edge of a flange. The area of the substantially triangular flgure XLZ represents the quantity of metal which will be forced into the adjacent end half of the flange under prior art practice and cause wrinkles therein. That half of an elevation :22, Fig. 3, which is adjacent the figure XLZ has a surface area greater than its projected plan area by an amount which is substantially equal to the area of XLZ. The displacement elevations then around these recesses will utilize the metal which would otherwise appear in the flange walls and cause folds and wrinkles therein.

Fig. 11 shows an inset or joggled rib section or portion like that designated at "ID in Fig. 1. It has a web 40 and a flange 4|. The flange 4| has an inset portion 4la. In forming this flange in the manner heretofore practiced, wrinkles form in the S bend at 42 at the end of the inset portion 4|a of the flange. To accommodate the excess metal which will otherwise appear as wrinkles at 42, an elevated ridge or facet 43 is formed in the web. a

Fig. 12 shows a forming block 44 for producing the inset rib portion shown in Fig. 11. The face 45 of the block 44 is ridged upwardly at 46. The difference between the surface area of the top front and rear side walls of the ridge 48 and its plan area if projected upon the face 45 of the block is substantially equal to the area of a horizontal section of the inset space 41 between the flange portion Ma and the flange 4| if extended.

As described above in connection with the forming of a nose rib, the ridge 46 in the face 4! of the block forms the ridge 43 in the web 40 of the inset rib section, thereby entirely eliminating the formation of wrinkles inthe flange of the rib section.

Iclaim as my invention: 4

1. man integrally constructed flanged sheet metal product of the kind formed by pressing a being substantially equal to the area in the plane of the web between said inset section of the periphery of the web and the extended line of said straight section, said ridge projecting out of the plane of the web in a direction generally opposite to the direction of projection of said flanges.

2. A process for making a sheet metal article, including the steps of: bending one portion of a plate with respect to another portion thereof to form a first wall and a second wall at an angle thereto, along a line between said walls forming a non-rectilinear periphery for said first wall substantially in a single plane; while forming a concavo-convex bulge in said first wall at said periphery projecting from said first wall in a direction opposite to the direction of projection of said second wall with respect to said first wall, and drawing suflicient metal from said second wall in the zone of said non-rectilinear portion into said bulge to prevent wrinkling of said second wall.

3. A structural piece having a body portion with a marginal flange extending along an edge thereof, said flange having a jog formed therein so that the flange presents two extensions disposed in substantially parallel planes connected by the jog, said jog operating to develop an excess of material in the body portion of the piece adjacent the extension of the flange that is projected inwardly on the body portion, said body portion having an area offset out of its plane in a direction opposite to the projection of said flange, to accommodate excess material from the flange.

4. A process of fabricating a flanged article from a sheet metal plate, comprising the steps of:

holding th central portion of the plate stationary; forming a convexo-concave bulge in said central portion starting at a predetermined marginal line thereof and extending back into the inner area thereof from metal drawn solely from the marginal area of said plate; and bending said marginal area of said plate along a non-rectilinear line at an angle to the web portion to form an unwrinkled, uncorrugated flange around the periphery of the web projecting in a direction opposite to the direction of projection of said. bulge.

5. A process of fabricating a one-piece metallic articlehaving a sharply curved, marginally depending flange-from an entirely flat sheet metal plate having a retum-curved margin, including: positioning said plate against a forming instrumentality with said margin overhanging same;

applying a compressive force perpendicularly tothe plate in predetermined peripherally spaced locations in the plate at said margin and drawing metal solely from aid overhang into said-predetermined locations, and forming surface areaincreasing convexities on the exterior face of the plate from said metal drawn from said overhang; holding said so formed plate stationary to form a web, and bending'said overhang at an angle to said web to form a sharply curved, small radius flange having all points of each face thereof lying in a faired-curve, unwrinkled surface and projecting in a direction opposite to the direction of projection of said area-increasing convexities.

6. A process of fabricating a one-piece metallic article-having a sharplycurved marginally depending flange-from an entirely flat sheet metal plate having a return-curved margin, including: positioning said plate against a forming instrumentality with said margin overhanging same; applying a compressive force perpendicularly to the plate in predetermined peripherally spaced locations in the plate at said margin and drawing metal solely from said overhang into said predetermined locations, and forming surface area-increasing convexities on the exterior face of the plate from said metal drawn from said overhang; holding said so formed plate stationary to form a web; and bending said overhang at an angle to said web to form a sharply curved,

small radius flange having all points of each face thereof lying in a faired-curve unwrinkled surface and projecting in a direction opposite to the direction of projection of said area-increasing convexities, the amount of metal drawn into, and the outward convex extent of said protuberances being preproportioned to the radius of curvature of said flange and to the peripheral spacing of said protuberances.

-7. A process of fabricating a one-piece metallic article-having a sharply curved marginally determined locations, and forming surface area-increasing convexities on the exterior face of the plate from said metal drawn from said overhang;

holding said so formed plate stationary to form a web; and bending said overhang at an angle to said web to form a sharply curved, small radius flange having all points of each face thereof lying in a faired-curve, unwrinkled, uncorrugated surface and rojecting in a direction opposite to the direction of projection of said area-lncreasing convexities, the amount of metal to be drawn from said overhang being predetermined to in-" crease the exterior area and metallic content of said web by an amount equal to the decrement in area and volume of each portion of the flange that lies subadjacent to the center line of each convexity.

8. In an integrally constructed flanged sheet metal product of the kind formed by pressing a sheet metal plate over a former block, and bending the marginal portions of the plate towardthe sides of the block; a web having a curvilinear peripheral edge portion; a plurality of flanges depending from said curved peripheral portion and spaced from each other toform gaps; and a localized concavo-convex protuberance on said web opposite each of said aps, starting at said curved edge portion and extending back into the inner area of the web and including metal crowded out of the flange when the sam is formed, said pro-v tuberance projecting out of the plane of the web in a direction generally opposite to the direction of projection of said flanges.

9. In' an integrally constructed flanged sheet metal product of the kind formed bypressing a sheet metal plate over a former block, and bending the marginal portions of the plate toward the sides of the block; a web having a curvilinear peripheral section; a plurality of flanges depending from said peripheral section and spaced from each other to form gaps between the same, said web having a marginal cut-out opening communicating with each of said gaps; and a. concavo-convex protuberance on said web contiguously surrounding each of said openings projecting from the plane of the web, starting at the edge of the web and fairing off downwardly in each direction from said opening along the periphery of said web, said protuberance projecting out of the plane of the web in a direction generally opposite to the direction of projection of said flanges.

10. In an integrally constructed flanged sheet metal product: a web having a periphery including a non-rectilinear portion; a flange depending from said web along at least the non-rectilinear portion; and a localized convex protuberance v on said web starting at the non-rectilinear porin a direction generally opposite to the direction of projection of said flange.

ORVIILE A. WHEELON. 

